A number of relatively common breathing disorders are treated by delivery of pressurized, breathable gas to a patient's airway. This is customarily done through the use of a mask. A mask is normally held in place over a patient's nose or face by one or more straps. The straps encircle the patient's head and are adjusted to create a gas tight seal between the mask and the patient's face. For example, as shown in FIG. 1, a nasal mask 10 includes a shell 12, forming a chamber with a seal 18. The seal 18 contacts the wearer's face forming the gas tight seal.
The patient's nasal area and face are complexly contoured and differ from patient to patient. Thus, during extended use, the mask may move relative to the patient's nose or face breaking the gas tight seal or becoming uncomfortable. The customary response is for the patient to tighten the mask's straps, which may cause the mask to push too strongly on the soft tissue surrounding the patient's nose or on the patient's face.
FIG. 2 shows an example of how this problem was addressed in the prior art. As is described in more detail in U.S. patent application Ser. No. 09/979,972 filed Nov. 28, 2001, the constructed of a compliant and resilient material. Disposed along the perimeter 24, and only the perimeter 24 of the shell is a formable element 26. The formable element may be a wire made for a relatively soft metal such as aluminum or copper or other materials known to those skilled in the art. The formable element may be affixed to the surface of the shell or molded within the shell.
The formable element 26 can be constructed from any material that is formable and is capable of retaining the shape into which it is formed against the force of, for example, the resilient shell 22 trying to regain its memory shape. The combination of the compliant and resilient shell 22 and the formable element 26, having sufficient rigidity to hold the shell 22 in a selected configuration, produces a “custom-fit” as desired by a particular user. Because the shell 22 is compliant, the perimeter and overall configuration of the shell 22 can be reformed repeatedly, as necessary, by a particular user.
In use, this mask, as shown in FIG. 3, tends to crease along a midline C running from the point 32 at which the mask contacts the bridge of the patient's nose to the point 33 at which the mask contacts the patient's face in the middle of the patient's chin. This crease causes the mask to become uncomfortable and causes the gas tight seal to be broken.